1. Field of the Invention
The present invention relates to an oil-impregnant sintered bearing in which a bearing main body is impregnated with lubricating oil for improving lubrication with a rotating axis member which runs through an internal diameter of the bearing, and the manufacturing method thereof.
2. Related Art
An oil-impregnant sintered bearing is composed of a porous sintered metal, and is impregnated with lubricating oil prior to use. Consequently, the oil-impregnant sintered bearing can be used for a long period of time without being further oiled, has superior durability at high temperatures and low noise levels. For these reasons, it is widely used instead of a ball-bearing as a bearing for a rotating axis member.
This type of oil-impregnant sintered bearing comprises a cylindrical bearing main body of porous sintered metal, which an internal face is provided therein. A rotating axis member has a smaller diameter than the diameter of the internal face, and is inserted therein. Lubricating oil, which is sucked out from the great number of small pores which are buried in the bearing main body or opened in the surface of the internal face by the pump action accompanying the rotation of the rotating axis member, and a lubricating oil, which has been exuded by expansion caused by frictional heating, form an oil film at the section of the oil-impregnant sintered bearing which slides against the rotating axis member; this oil film supports the rotating axis member and protects it from damage such as burning.
However, in such an oil-impregnant sintered bearing, since even the sliding face, which the rotating axis member contacts while sliding, has a great number of pores which the lubricating oil is impregnated in, even when the oil film is formed between the rotating axis member and the sliding face, some of the lubricating oil leaks from the pores, reducing the oil pressure and allowing local contact between the rotating axis member and the sliding face. As a consequence, there are drawbacks in that the frictional coefficient with the rotating axis member increases, and burns on the like may occur.
An oil-impregnant sintered bearing 101 shown in FIG. 4 is a conventional proposal for dealing with these drawbacks. The oil-impregnant sintered bearing 101 having an internal diameter 104, which is provided in a bearing main body 103 of porous sintered alloy having internal pores, and a rotating axis member 102, which is inserted through the internal diameter 104. A sliding face 105 is provided by closing pores in one region in the periphery direction on the inner peripheral face of the internal diameter 104. This method for preserving the oil film stops the lubricating oil from leaking when the sliding face 105 contacts the rotating axis member 102, and prevents the reduction in oil pressure mentioned above.
However, as for the example disclosed in Japanese Patent Application, First Publication No. 4-307111, even when pores are closed in the inner peripheral face of a pressed powder body, obtained by pressure-forming of raw material powder, the pores sometimes re-open during sintering since tin and the like is included in the raw material powder. Consequently, oil seeps from the holes to the inside, and oil pressure decreases. Further, Japanese Patent Application, First Publication No. 5-180229 discloses technology for closing the pores in the inner peripheral face when plugging in a rod for forming the bearing at the time of post-sintering correction. However, this technology basically involves closing the pores which have appeared in the inner face, and cannot preserve the oil film since the surface layer may be broken by the oil pressure, allowing the oil to seep to the inside.
Further, Japanese Patent Application, First publication No. 8-28567 discloses technology which uses a welded material having no pores in one section of its inner peripheral face. However, since the welded material cannot contain lubricating oil, the capacity of lubricating oil which can be contained in the oil-impregnant sintered bearing is reduced.